ast-grep

AST Grep

Use this skill when text search would be noisy or unsafe.

Tools

• code_search(pattern, lang, path?, limit?) — find code by AST pattern
• code_rewrite(pattern, rewrite, lang, path?, dry_run?) — structural find-and-replace

Examples

• console.log($MSG) — find all console.log calls
• var $NAME = $VAL → const $NAME = $VAL — modernize var declarations
• catch ($ERR) { } — find empty catch blocks
• import $X from "lodash" — find imports from a specific module

Workflow

1. code_search(pattern, lang, path, limit=20) — narrow path, sample first
2. Inspect matches — verify pattern catches what you want
3. code_rewrite(pattern, rewrite, lang, path, dry_run=true) — preview changes
4. Review the dry run output
5. code_rewrite(pattern, rewrite, lang, path, dry_run=false) — apply
6. Read changed files, run formatting/tests

Prefer other tools when

• You need plain text, comments, or strings → grep
• You need type/symbol-aware results → LSP/symbol tools if available

Safety

• Always run dry_run=true before applying any rewrite
• Scope with path to avoid unintended matches in vendored/generated code
• Supported lang values: typescript, javascript, tsx, jsx, python, rust, go, java, c, cpp, csharp, ruby, swift, kotlin, lua, html, css, json, yaml
• After applying rewrites, read changed files and run tests/formatting before moving on

Troubleshooting

• No matches: verify lang is correct (e.g. typescript not ts), broaden pattern
• Too many matches: narrow path, add more structure to pattern, lower limit
• Pattern error: simplify — patterns must be valid syntax in the target language
• Wrong language: typescript ≠ tsx, javascript ≠ jsx — run separate passes